Conventionally, it is known that reflecting mirrors are provided in an embodiment of optical switches. This type of optical switch has a movable mirror between an input optical fiber and two or more output optical fibers. In this optical switch, the angle of the movable mirror is controlled according to the control signal that specifies the output optical fiber to which an optical signal is output. Generally, the angle of movable mirror is controlled by drive voltage. In this case, a desired output optical fiber is selected by controlling the drive voltage. Note that MEMS (Micro Electro Mechanical Systems) are sometimes used in the manufacturing process of optical switches in recent years.
In such an optical switch, the correspondence relationship between drive voltage and the rotation angle of a movable mirror changes, generally, due to the temperature or the age-related deterioration. In other words, for example, if the temperature around the optical switch changes, the rotation angle of a movable mirror is misaligned from a target angle, and thus light beam reflected by the movable mirror is not appropriately guided into an output optical fiber. In this case, the loss in the optical switch becomes large. For this reason, the configuration of dynamically correcting the correspondence relationship between drive voltage and the rotation angle of a movable mirror has been proposed.
As a related art, an optical switch in which a drive circuit provides drive voltage to a mirror unit, including a low-frequency superimposition circuit, a low-frequency detection unit, and a control circuit, has been proposed (for example, Japanese Laid-open Patent Publication No. 2003-29175). In such an optical switch, the low-frequency superimposition circuit superimposes a low-frequency signal on the drive voltage generated by the drive circuit. In other words, the mirror unit is driven by the drive voltage on which a low-frequency signal is superimposed. The low-frequency detection unit detects a low-frequency component from the output light that is reflected by the mirror unit. Then, the control circuit controls the drive voltage that is generated by the drive circuit based on the detected low-frequency component.
As another related art, the configuration for performing feedback control to reduce the alignment error between an input optical fiber and an output optical fiber has been proposed (for example, Japanese National Publication of International Patent Application No. 2005-500538).
As described above, configurations for dynamically adjusting a drive system of an optical switch has been proposed. However, in the related art, the angle sometimes cannot be adjusted appropriately depending on the rotation angle of a movable mirror. For example, in one related art, control is performed assuming that the rotation angle of a movable mirror changes linearly with respect to drive voltage. In this case, the angle of a movable mirror might not be adjusted appropriately, and thus the optical loss would be large in a region in which the drive voltage is large (i.e., the state in which the movable mirror has been largely rotated from an initial angle).